For high millimeter-wave frequencies (i.e., terahertz radiation), it is difficult to build adequate radiating structures. Typically, radiation is reflected within the package or substrate supporting the antenna, generating surface waves. At the edges of the package or substrate, the surface waves can generate parasitic currents that distort the wave pattern. To combat this problem, HISs have been employed to inhibit surface waves and generally prevent the parasitic currents that cause the wave pattern distortion.
Turning to FIGS. 1 and 2, an example of a conventional HIS 100 can be seen. This HIS 100 is generally comprised of an array of cells 102. Each cell 102 is generally comprised of a ground plane 106 (which typically underlies the entire array), via 108, and a plate 106. The plate 110 is part of a metallization layer (which can be formed of aluminum or copper) that is patterned to form the array. By using such an array, the reflection coefficient of the electric field has a zero phase, which causes the HIS to have a high impedance.
In FIGS. 3 and 4, another example of a conventional HIS 200 can be seen. Contrasting HIS 100 and HIS 200, HIS 100 has non-overlapping cells where the plates are generally hexagonal in shape, while HIS 200 employs lines of cells 202 and 204. As shown, the via 210 is slightly larger than via 204 so that the edge of plate 212 can overlap the edge of plate 208. By using this configuration, plates 208 and 212 are capacitively coupled or form a capacitor, which allowing the HIS 200 to be tuned to a lower frequency than HIS 100.
For HISs 100 and 200, however, there is great difficulty in producing an HIS that can be used for high millimeter-wave frequencies (i.e., terahertz radiation). Manufacturing processes (in many cases) may not have fine enough pitch resolution to produce the closely spaced cells for HIS 100 that would be functional in this desired frequency range, and the capacitive coupling for HIS 200 creates further complications as it tends to lower the resonant frequency. Therefore, there is a need for an HIS that can be used for high millimeter-wave frequencies (i.e., terahertz radiation).
Some other conventional structures are: U.S. Pat. Nos. 6,628,242; 6,670,932; 7,136,028; 7,136,029; 7,197,800; 7,423,608; 7,518,465; U.S. Patent Pre-Grant Publ. No. 2005/0134521; U.S. Patent Pre-Grant Publ. No. 2009.0201220; and European Patent No. EP1195847.